1. Field of the Invention
The present invention relates to a reluctance type rotating machine having permanent magnets, which is compact and capable of rotating at high speed and high outputs.
2. Discussion of Background
Recently, electric propulsion systems such as a hybrid automotive vehicle, an electric vehicle and an electric rail car has rapidly been developed. These electric propulsion systems require a wide range variable is speed operation property, high efficiency and reliability in high temperature. A permanent magnet type rotating machine has been used for the electric propulsion system because of its wide range variable speed operation property at constant torque operation and high output property and high efficiency in wide speed range. However, the efficiency of the permanent magnet type rotating machine is deteriorated at low load operation. In view of these circumstances, lots of engineers are paying attention to a reluctance type rotating machine.
As shown in FIG. 1, a reluctance type rotating machine comprises a stator 1 having armature windings 2 and a rotor 3 having an uneven core 4 since the rotating machine does not require coils for forming a field system about the rotor 3. Therefore, the reluctance type rotating machine is simple in structure and low in price.
Because of unevenness of the rotor 3, the reluctance type rotating machine exhibits small magnetic reluctance at projection portions 5 of the rotor 3 and large magnetic reluctance at recess portions 6. That is, there is a difference between magnetic energy stored about a gap over the projection portion 5 and the magnetic energy stored about another gap over the recess portion 6. Note, the magnetic energy can be stored by sending an electric current to the armature windings 2. Owing to this difference in magnetic energy, the rotating machine can produce power output.
Meanwhile, although both the projection portion 5 and the recess portion 6 are geometrical elements in the shown rotating machine, the rotor 3 may be modified so as to have magnetic unevenness, for example, different magnetic reluctance or different magnetic flux density distributions depending on positions in the rotor.
As another high-performance rotating machine, there exists a permanent magnet type rotating machine. Although this rotating machine includes armatures similar to that of the reluctance type rotating machine, a rotor is provided, on the whole periphery of a core, with permanent magnets.
Due to the unevenness on the core, the reluctance type rotating machine has different magnetic reluctance depending on rotational positions of the rotor. With the change of the magnetic reluctance, the magnetic energy also varies to produce the output power.
In the conventional reluctance type rotating machine, however, the increasing of currents causes a locational magnetic saturation to be enlarged at the projection portions 5. Thus, the enlarged magnetic saturation also causes magnetic fluxes leaking to the recess portions 6 between poles to be increased, so that effective fluxes are decreased while lowering the output power.
On the other hand, as another high-powered rotating machine, there is a permanent magnet type rotating machine using "rare metal" permanent magnets exhibiting high magnetic energy products. However, since the permanent magnets have to be disposed on the whole surface of a rotor core, the rotating machine requires a great number of permanent magnets, disadvantageously.
Moreover, in the permanent magnet type rotating machine, there is a problem that interlinkage fluxes to an armature increase to make iron loss increased at low load operation.